Heat exchangers of the concern of this invention provide for flow of fluids of different temperature in a physically separated but heat transfer relation. For example, in a tubular heat exchanger, a first fluid is caused to flow through a tube or assembly of tubes while at the same time a second fluid is caused to flow over and around the tube or assembly of tubes. A transfer of heat between the fluids takes place through the tube wall or walls. A surrounding shell and header plates and manifolding means at the header plates are usually provided in order that the fluids may be confined and controlled in their flow and in order to enforce separation of the fluids.
It is frequently undesirable that the fluids be allowed direct physical contact with one another, and an optimal design criterion stipulates that no single leak, caused either by fracture of a tube wall or failure of a tube-to-header joint shall result in mixing of the fluids. Leak protected heat exchangers are known in the prior art (an example being that of U.S. Pat. No. 3,825,061, dated July 23, 1974), but devices meeting the single leak test above mentioned are unknown. In particular, are tubular heat exchangers unknown in which neither a tube wall fracture nor a failure of a tube-to-header joint will result in direct physical contact between separated fluids.